Dielectric heating means



Jan. 21, 1-964 J. F. DREYER, JR 3,118,999

DIELECTRIC HEATING MEANS Filed Aug. 14, 1961 2 Sheets-Sheet l FIG INVENTOR. JOHN F. DREYER JR.

Wm? WM 1964 J. F. DREYER, JR 3,118,999

' DIELECTRIC HEATING MEANS Filed Aug. 14, 1961 2 Sheets-Sheet 2 FIG 3 JNVENTOR. JOHN F. DREYER JR.

BY gm WM United States Patent 3,118,99Sl DIELECTRIC HEATING MEANS John F. Dreyer, Jan, Baldwin, N.Y., assignor to Hahn instrument Co., Inc, Glen Head, New York Filed Aug. 14, 1961, Ser. No. 131,443 3 Claims. ((li. 219-10.75)

This invention relates to dielectric heating means and more particularly to such means adapted for sealing plastic containers.

One of the primary problems involved in such apparatus is that of frequency control, since the FCC. has allocated :a frequency of 27120 11160 mc. Conventional apparatus generally uses two output tubes to obtain the required power. These tubes are generally connected in parallel with the grids of the tubes connected together. This arrangement prevents proper balance of the load on the output tubes and also gives rise to the generation of parasitic oscillations, both of which conditions are objectionable.

The present invention resolves these difiiculties by operating the two output tubes with separate :grid connections so that the exact balance of the load may be adjusted, parasitic oscillations may be eliminated, and the frequency may be accurately controlled.

Accordingly a principal object of the invention is to provide new and improved dielectric heating means.

Another object of the invention is to provide new and improved dielectric heating means having means to prevent parasitic oscillations.

Another object of the invention is to provide new and improved dielectric heating means having a pair of output tubes and including means to balance the load between the two tubes.

Another object of the invention is to provide new and improved high frequency dielectric heating means having means to accurately adjust the frequency.

Another object of the invention is to provide new and improved high frequency dielectric heating means comprising an oscillator having a pair of vacuum tubes, a tunable cavity comprising a hollow conductive member, a conductive pipe mounted coaxial-1y inside said hollow member, a first piston bracket slidab-ly mounted inside said hollow member and electrically connected to said cavity with spring fingers, means to adjust the position of said first bracket, a pair of vacuum condensers mounted on said first bracket, the other ends of said condensers being slidably connected to said hollow pipe, the plates of said vacuum tubes being each connected through a suitable blocking capacitor to one of said other ends of said vacuum condensers, means to separately adjust the load on said vacuum tubes, an output connection slidably connected to said pipe, and a movable sewing die connected to said output connection.

These and other objects of the invention will be apparent in the following specifications and drawings of which:

FIG. 1 is a schematic circuit diagram of an embodiment of the invention.

FIG. 2 is a detail view of the tunable cavity of the embodiment of FIG. 1, and

FIG. 3, is a circuit diagram of the frequency measuring means of the embodiment of FIG. 1.

Referring to the figures, the invention generally comprises a high frequency oscillator including a pair of high power vacuum tube triodes 1 and 2, each having a plate, a grid, and a cathode and being connected to a tuned cavity 3 in a modified T.N.T. type circuit. An inductance 4, which may comprise a copper pipe is mounted coaxially in the cavity 3 which may have a square cross section. A pair of vacuum condensers 5 and 6 are mounted on a piston type bracket which is slidably and adjustably mounted in the cavity 3 by means of the adjustment screw 8 and adjustment knob 10. The bracket 7 is connected to the interior sides of the cavity 3 by means of spring fingers 11 and 12. The other ends of the vacuum condensers 5 and 6 are connected to the inductive pipe 4 by means of a second bracket 13 which is connected to the pipe 4 by means of spring finger contacts 14, 15. The output to the load is provided by a sliding contact v16 which is connected to the inductive pipe 4-.

The load voltage is adjusted by means of the threaded rod 45, having a knob '47 upon which is mounted a travelling nut 46 to which is fixedly mounted the contact 16 which extends through a slot in the pipe 4. The load voltage is adjusted by turning the knob 47 causing the nut 46 and contact 16 to slide up and down the pipe 4. The load may be a conventional die D mounted in a movable press and adapted to press the workpiece W against a base member 17.

The plates of the vacuum tubes 1 and 2 are concented to the bracket 13 by means of the leads 2% and 21 which extend through apertures in the side of the tunable cavity 3. DC. blocking condensers are inserted in the series with the leads 2d and 21. The plates of the tubes 1 and 2 are connected to the B+ supply which may be for instance 4,0 OO volts, through conventional R.F. chokes 22 and 23. The grids of the tubes 1 and 2 are not connected directly together, but are connected to separate bias adjustment means 40 and 4 1 respectively for balancing the load between tubes 1 and 2. Grid leak bias is provided by resistors 27 and 28.

The cathodes of the tubes 1 and 2 are connected to filament transformers and 26, the primary coils of which are connected to a source of AC. voltage, for instance 120' volts. The centers of the secondary coils of the filament transformers are connected to ground through separate cathode bias adjustments provided by potentiometers 42 and 43 respectively.

The oscillator comprising the vacuum tubes 1 and 2 operates as a modified T.N.T. circuit with the feed back provided thnough the plate to grid capacity.

FIG. 3 shows a schematic diagram of a Travers type frequency measuring device 34 of FIG. 1 'which is used to adjust the frequency to the desired operating frequency. The input to the frequency meter 30" may be a coaxial pick-up 31 which is fed thuoug-h a limiting tube 32 to a pair of discriminators 33 and 34, one of which is tuned slightly above the desired frequency, and the other of which is tuned slightly below the desired frequency. The out-puts of the discriminators are fed through diodes 35 and 36 to a zero center meter 37 which will indicate zero when the cavity 3 is tuned to the proper frequency and which vvill indicate or if the cavity 3 is not properly tuned.

In operation, the device is set up by turning on the povver and allowing the equipment to warm up to a stable condition. A workpiece W is placed in the sealing die D and the press is closed with the contact 16 adjusted to give a relatively low output voltage.

The adjustment knob 10 is then turned to adjust the frequency of the cavity according to the meter 37.

The load voltage is then adjusted by moving the contact 16 up the pipe 4 to the optimum voltage for the work by trying a few workpieces. The frequency is then readjusted by means of the knob 10, and the apparatus is in condition for operation.

The load on the two vacuum tubes 1 and 2 may be balanced by adjusting the grid bias on the two vacuum tubes 1 and 2.

Due to the fact that the grids of tubes *1 and 2 are not directly connected together, the loads may be balanced and also the possibility of undesired spurious parasitic oscillation is minimized. The apparatus may then be operated in a conventional manner by causing a movement of the press to connect the 13+ voltage through switch 39 for a pulse of approximately one second to seal each workpiece.

The vacuum tubes 1 and 2 may be conventional type 9902 tubes which operate at 4,000 volts plate voltage with a rated output of /2 ampere. The vacuum condensers may be conventional 100 mmf. condensers.

The tuned cavity 3 is preferably about 19 inches along its axis and the coaxial pipe 4 may be of /4 inch copper tubing approximately 12- inches long. All of the other components may be conventional elements having the usual conventional values.

Many modifications may be made by those desiring to practice the invention, and various mechanical equivalents may be used in place of the particular means in this embodiment without departing from the scope of the invention, which is defined by the following claims.

I claim:

1. Dielectric heating means comprising an oscillator having a pair of triode vacuum tubes, a tunable cavity comprising a hollow conductive member substantially less than a quarter wavelength long, a conductive pipe mounted coaxially inside said hollow member, a first bracket slidably mounted inside said hollow member and electrically connected to said cavity with spring fingers, frequency adjusting means to adjust the position of said first bracket, two or more vacuum condensers mounted on said first bracket, the other ends of said condensers being slidably connected to said hollow pipe, the plates of said vacuum tubes being each connected to one of said other ends of said vacuum condensers, separate grid bias means connected to the grids of each of said vacuum tubes, and an adjustably output connection slidably connected to said pipe, ta mowable sealing die connected to said output connection.

2. In dielectric heating means of the type having an oscillator including a pair of triode vacuum tubes; a tunable cavity comprising a hollow conductive member substantially less than a quarter Wavelength long, a conductive pipe mounted coaxially inside said hollow member, a first bracket slidably mounted inside said hollow member and electrically connected to said cavity with spring fingers, means to adjust the position of said first bracket, a pair of vacuum condensers mounted on said first bracket, the other ends of said condenser being slidably connected to said hollow pipe, the plates of said vacuum tubes being each connected to one of said other ends of said vacuum condensers, an output connection slidably connected to said pipe, and separate grid bias means connected to the grids of each of said vacuum tubes to balance the loads on said vacuum tubes.

3. In dielectric heating means of the type having an oscillator including a pair of triode vacuum tubes, each having a plate, -a grid, and a cathode; a tunable cavity comprising a hollow conductive member substantially less than a quarter Wavelength long, a conductive pipe mounted coaxially inside said hollow member, a first piston bracket slidably mounted inside said hollow member and electrically connected to said cavity with spring fingers, means to adjust the position of said first bracket, two or more vacuum condensers mounted on said first bracket, the other ends of said condensers being slidabl y connected to said hollow pipe, the plates of said vacuum tubes being each connected to said other ends of said vacuum condensers, an output connection slidably connected to said pipe, means to move said output connection on said pipe, separate bias adjustment means connected to the cathodes of said triode vacuum tubes, and separate unconnected means connected tothe grids of said vacuum tubes to balance the loads on said vacuum tubes.

References Cited in the file of this patent UNITED STATES PATENTS 2,169,305 Tunick Aug. 15, 1939 2,465,102 Joy Mar. 22, 1949 2,765,387 Wilson Oct. 2, 1956 

1. DIELECTRIC HEATING MEANS COMPRISING AN OSCILLATOR HAVING A PAIR OF TRIODE VACUUM TUBES, A TUNABLE CAVITY COMPRISING A HOLLOW CONDUCTIVE MEMBER SUBSTANTIALLY LESS THAN A QUARTER WAVELENGTH LONG, A CONDUCTIVE PIPE MOUNTED COAXIALLY INSIDE SAID HOLLOW MEMBER, A FIRST BRACKET SLIDABLY MOUNTED INSIDE SAID HOLLOW MEMBER AND ELECTRICALLY CONNECTED TO SAID CAVITY WITH SPRING FINGERS, FREQUENCY ADJUSTING MEANS TO ADJUST THE POSITION OF SAID FIRST BRACKET, TWO OR MORE VACUUM CONDENSERS MOUNTED ON SAID FIRST BRACKET, THE OTHER ENDS OF SAID CONDENSERS BEING SLIDABLY CONNECTED TO SAID HOLLOW PIPE, THE PLATES OF SAID VACUUM TUBES BEING EACH CONNECTED TO ONE OF SAID OTHER ENDS OF SAID VACUUM CONDENSERS, SEPARATE GRID BIAS MEANS CONNECTED TO THE GRIDS OF EACH OF SAID VACUUM TUBES, AND AN ADJUSTABLY OUTPUT CONNECTION SLIDABLY CONNECTED TO SAID PIPE, A MOVABLE SEALING DIE CONNECTED TO SAID OUTPUT CONNECTION. 